The present invention relates to a cold pressure-welding apparatus.
Conditions of cold pressure-welding are controlled according to the pressure-welding load exerted on the pressure-welding part of an object, i.e. the amount of deformation of said part.
FIG. 1 shows a load-displacement curve which represents the relationship between a pressure-welding load L(X) exerted on an object to be pressure-welded and a displacement X of the pressure-welding part of the object. In the conventional method, a yield load LO at a yield point 4 of the material of each object having a specific size is calculated. Here, the term "yield point" is used in the sense of strength of materials and is located at the boundary between an initial linear elastic deformation part 2 and a non linear plastic deformation part 3 of the load-displacement curve. An optimum load LA which holds a predetermined relationship with the yield load LO is then determined. Thus, cold pressure welding is performed utilizing this optimum load LA as the pressure welding stop condition if conditions remain the same. However, in practice, the load-displacement curve changes from one pressure-welding object to another due to the fluctuations in the thickness of the pressure-welding object or nonuniform heat-treatment. For this reason, the initially set optimum load LA frequently becomes unsuitable. In some cases, the working rate becomes too high thus degrading the strength of the overall pressure-welding objects, or the working rate becomes too low thus decreasing the pressure-welding strength.